Air conditioning units are commonplace in many of today's residential and commercial structures. These systems generally employ a conduit filled with a thermally conductive coolant, such as freon, which is subjected to at least two heat exchanges that transfer the heat from inside the structure to the outside. The conduit transfers high pressure, low temperature liquid coolant to an expansion valve wherein the pressure of the coolant is reduced, thereby lowering the temperature of the coolant. This low pressure, low temperature coolant is then directed into an evaporator, which is generally a system of coiled tubes, that act as a heat exchanger. More specifically, the fluid in the evaporator is exposed to warm return air that has been circulated through the structure, thus transferring the heat of a warm return air to the coolant in the evaporator. The now cooled air is directed through the structure, in various ways known in the field, where it will be warmed by the atmosphere into where it has been introduced and subsequently returned to the evaporator. The process of evaporation changes the coolant in the evaporator from a liquid to a vapor. That vapor is directed to a compressor, which operates on the vapor to increase the pressure and temperature thereof. The high temperature, high pressure vapor exiting the compressor is then directed to a condenser that transforms the vaporized coolant into a low temperature liquid. The condenser is much like the evaporator, in that a series of coils are provided to form a heat exchanger. A fan adjacent to the condenser blows ambient air past the high temperature, high pressure vaporized coolant in the coils, thus transferring the heat energy of the various coolant to exhaust air, transforming the vaporized coolant back into a liquid to complete the coolant loop.
The evaporator of the air conditioning system is designed to convert liquid coolant to vapor such that at the exit, or low pressure side of the evaporator contains only vaporized coolant. More specifically, it is desirable to maintain an operating condition wherein the evaporator efficiency changes liquid coolant into vapor such that the temperature at the low pressure end of the evaporator is the saturation temperature of the coolant. As those in the field will appreciate the saturation temperature of the coolant is dependent on various properties of the parts where coolant employed and is generally considered the temperature at which the coolant changes from a vapor to a liquid.
Air conditioning systems often do not operate at peak efficiency. For example, the liquid coolant may be evaporated too quickly, prior to the exit of the evaporator, such that a portion of the evaporator contains superheated coolant vapor. This condition results in a drop in efficiency of the overall air conditioning system since reduced heat transfer occurs between the warm return air and the fluid and/or vapor in the evaporator. Alternatively, if the heat transfer is insufficient to boil all the coolant prior to it reaching the evaporator exit, fluid may be directed into the compressor which is detrimental to its overall operation.
In order to maintain optimum cooling efficiency, technicians are often employed to periodically monitor and maintain air conditioning systems. Efficiency is commonly assessed by monitoring the superheat temperature of the air conditioning unit which, as those in the field appreciate, is equal to the suction temperature of the system minus the saturation suction temperature. The suction temperature is the temperature of the low pressure side of the system, usually but not always measured at the exit of the evaporator. The saturation suction temperature is a function of the pressure at the low pressure end of the evaporator. More specifically, the pressure at the evaporator exit may be monitored, and depending on the type of coolant in the system, the saturation suction temperature may be calculated.
It is considered by those in the field desirable to have an optimum superheat condition in the unit, which is the temperature of the coolant at the low pressure end of the evaporator. If the superheat temperature is too high, the use of the coil is not maximized, wherein the fluid evaporates too quickly and efficient heat transfer is not achieved. Alternatively, if the superheat temperature is too low, the coolant is not efficiently evaporating in the coil and coolant may then be transferred to the compressor, which is detrimental to the components therein. A superheat condition of zero is ideal, since that indicates the suction temperature of the system is equal to the temperature at which the coolant changes from a liquid to a vapor, thus indicating that the liquid coolant was efficiently transferred to vapor coolant at the proper place in the coolant loop. However, one skilled in the art will appreciate that this condition is not easily attained due to inefficiencies of any air conditioning system, such that acceptable superheat ranges for each air conditioning unit are generally used.
Devices of the prior art monitor the suction temperature and the suction pressure of air conditioning systems. They often also monitor other temperatures around the air conditioning coolant loop to assess the efficiency of the system. However, monitors of the prior art are commonly one-piece units such that a technician must make judgments where to place temperature and/or pressure sensors. In addition, a plurality of readings at various locations are usually required. In the prior art, these measurements are taken in series by a technician. This process is both time consuming to the technician and fosters inaccuracies in the superheat calculation, as measurement values may change due to the passage of time during the data collection process.